From the Guidelines
Hypogonadism can result from several glandular causes, including primary testicular failure, pituitary disorders, and hypothalamic dysfunction, and MRI is primarily indicated for suspected secondary hypogonadism when blood tests show low testosterone with inappropriately normal or low gonadotropins (LH/FSH) 1.
Glandular Causes of Hypogonadism
- Primary causes involve direct testicular damage from conditions like Klinefelter syndrome, orchitis, trauma, or chemotherapy.
- Secondary hypogonadism stems from pituitary issues such as tumors (prolactinomas, non-functioning adenomas), infiltrative diseases, or hypopituitarism.
- Tertiary hypogonadism involves hypothalamic dysfunction from Kallmann syndrome, idiopathic hypogonadotropic hypogonadism, or acquired causes like stress or medications.
Role of MRI in Hypogonadism
- The MRI should focus on the pituitary and hypothalamic regions with thin-slice, contrast-enhanced imaging to detect microadenomas, macroadenomas, empty sella syndrome, or other structural abnormalities.
- This imaging is crucial when laboratory findings suggest central hypogonadism, especially with symptoms of mass effect like headaches or visual disturbances, or when other pituitary hormone abnormalities are present.
- MRI findings help guide treatment decisions, as pituitary tumors may require surgical intervention before hormone replacement therapy is initiated, while primary hypogonadism typically doesn't require MRI evaluation 1.
Diagnostic Approach
- In men with diabetes who have symptoms or signs of hypogonadism, consider screening with a morning serum testosterone level 1.
- Further testing (such as luteinizing hormone and follicle-stimulating hormone levels) may be needed to distinguish between primary and secondary hypogonadism 1.
- In men who have total testosterone levels close to the lower limit, it is reasonable to determine free testosterone concentrations either directly from equilibrium dialysis assays or by calculations that use total testosterone, sex hormone binding globulin, and albumin concentrations 1.
From the Research
Glandular Causes of Hypogonadism
- Hypogonadism can be caused by primary (testicular) or secondary (pituitary-hypothalamic or central) factors 2
- Secondary hypogonadism is the result of a dysfunction within the hypothalamus and/or pituitary 3
- Pituitary incidentalomas are common, and patients with microprolactinoma are more likely to present with symptoms of sexual dysfunction while those with macroprolactinoma are more likely to present with symptoms of mass effect 2
Use of MRI in Diagnosing Hypogonadism
- Pituitary magnetic resonance imaging (MRI) may be necessary when clinically indicated, especially in cases where gonadotropins are low or inappropriately normal 2
- The prevalence of structural pituitary abnormalities by MRI scanning in men presenting with isolated hypogonadotrophic hypogonadism is significant, with 16.4% of men having abnormal imaging studies 4
- However, the yield of identifiable abnormalities on pituitary MRI is quite low, and it is not warranted in all patients with hypogonadotropic hypogonadism 5
- Anatomic lesions are likely to be present only when low levels of total testosterone (<5.2 nmol/L) are found concomitantly with high levels of prolactin and/or low insulin-like growth factor 1 standard deviation score (IGF-1 SDS) 5
Correlation between MRI Findings and Biochemical Parameters
- There is no correlation between testosterone level and the presence of pituitary anomalies 6
- Patients with raised prolactin had higher number of abnormal MRI findings and adenomatous lesions compared to men with normal prolactin 5
- Multivariate logistic regression showed an association of abnormal pituitary MRI with IGF-1 SDS and prolactin 5